Talha, from UI you can't delete an area and its subcategories. In fact, I don't think it is a good idea to delete any area/category as that would leave some existing objects pointing to nowhere if those objects point to the area/category
before. What is recommended is to make them inactive. If you have a few, you can do this one by one from web interface; if you have a lot, you could consider using pdm_extract and pdm_load. Thanks _Chi